1. Field of the Invention
The present invention relates to an internal combustion engine having an individually controlled fuel injection valve for each cylinder, and more particularly to a control apparatus for an internal combustion engine for preventing contamination of exhausted gas when some of the cylinders are misfired.
2. Prior Art
Various means for preventing the exhaust gas of an internal combustion engine from being contaminated have been known. Fuel injection methods for internal combustion engines of automobiles include the multi-point method in which the fuel is simultaneously supplied to the respective cylinders by means of a single fuel injection valve provided upstream of a branch point of an inlet manifold and the multi-point method in which each cylinder is individually supplied with fuel by means of an exclusive fuel injection valve. Trend is that a multi-point method injection pump is commonly employed as a useful means in a fuel system. The multi-point method is advantageous in distributing the fuel to the respective cylinders as compared to the single point method. The multi-point method is of a construction in which the fuel is injected to the intake port of the associated cylinder, and therefore very little amount of fuel is deposited to the wall surface of the manifold, ensuring clean exhaust gas as well as good control effect.
With the multi-point fuel injection pump, the excellent performance thereof permits clean exhaust gas to be exhausted while it is normally operating. However, when any one of the cylinders is misfired due to abnormal conditions in the engine, the fuel system, or the firing system, a large amount of unburned gas mixture is exhausted to cause increased environmental contamination.
In the case where the engine for the automobiles is provided with a catalyst converter in the exhaust system for purging the exhaust gas, the unburned air-fuel mixture contacts with the catalyst to cause oxidation of the gas, which in turn causes an increase in temperature of the catalyst. Particularly, if only one of a plurality of cylinders is misfired, the driver may not become aware of the misfiring, in which case not only the exhausted gas is extremely contaminated but also the temperature of the catalyst increases to an unusual point. This is a potential danger that may damage the catalyst.
To eliminate the problem described above, for example, Japanese Laid Open Patent Publication No. 61-23876 discloses a misfiring detecting method in which pressure sensors are disposed in the combustion chambers to detect and indicate misfiring by comparing the combustion pressures at two angular positions of a crank immediately before and after the top dead center of compression stroke.
The prior art method disclosed in Japanese Laid Open Patent No. 61-23876 is directed only to detecting and indicating the misfiring. Thus the rise in temperature of the catalyst and exhaust of unburned air-fuel mixture cannot be prevented unless the engine is immediately stopped. The automobile may continue to be driven till it arrives at a repair shop even though the misfiring is indicated to the driver for warning. The contamination of environment and overheat and damage of the catalyst during the trip to the repair shop remain unsolved.